A disc brake system of a motor vehicle is used to slow down the speed of the vehicle, or during parking to maintain the position, especially when the motor vehicle is parked uphill or downhill and the user exits the driver's seat.
During parking, a pad supported by a caliper or brake shoe fixed to the vehicle chassis is brought into contact with a rotating metal disc fixed to a type of the motor vehicle and applies a load, preferably constant, upon the disc itself. In particular, when the disc brake operates as a parking brake, it may happen that during a long or even very long stop in a moist or particularly wet environment electrochemical phenomena of corrosion start, in particular on the interface of the disc with the pad. This involves a corrosion impression which tends to damage the disc and causes adhesion between the friction material of the pad and the disc that can prevent the detachment and therefore blocks the vehicle in the parking position.
It was found that the corrosion and adhesion are higher when the friction material comprises powders with low or no metal content and high amounts of thermosetting polymeric materials. Said drawback is particularly felt since the current regulations provide the use of friction materials comprising polymer powders which are proving to be more ecological compared to conventional friction powders, for example those made of copper powder.